The present invention relates to a method for the preparation of a high-porosity adsorbent loaded with crystalline hydrous zirconium oxide that can selectively adsorb ions of fluoride, arsenic, phosphate and the like from an aqueous medium.
It is reported in Inorganic Chemistry, volume 3, page 146 (1964) that crystalline hydrous zirconium oxide can be obtained by a heat treatment of the hydrous zirconium oxide formed by the hydrolysis reaction of a zirconium salt using an alkali.
It is also reported in Inorganic Ion Exchange Materials, CRC Press, page 141 (1981) that the hydrous zirconium oxide prepared in the above described manner is a stable compound hardly soluble in any acids, alkalis and organic solvents and hardly susceptible to oxidation and reduction and exhibits a specific ion exchange behavior to adsorb fluoride, arsenic and phosphate ions selectively from an aqueous medium.
Since the hydrous zirconium oxide obtained by the above mentioned method is usually in the form of a fine powder, difficulties are encountered in handling thereof when the powder is intended to be employed in a specific ion exchange process involving adsorption and desorption of the ions and regeneration of the adsorbent.
In order to overcome the above mentioned disadvantages of the conventional hydrous zirconium oxide, a proposal is made in Japanese Patent Kokai 2-211244 for a method of obtaining hydrous zirconium oxide supported on a porous carrier material by a method in which, for example, a porous resin is impregnated with a tetraalkoxy zirconium which is subjected to an in situ hydrolysis reaction to be converted into hydrous zirconium oxide as supported on the carrier material. This method, however, involves a practical disadvantage that, if not to mention the expensiveness of the tetraalkoxy zirconium used as the starting material, the hydrous zirconium oxide formed by the hydrolysis reaction of a tetraalkoxy zirconium is in an amorphous form so that the hydrous zirconium oxide is easily leaked out of the pores of the carrier material resulting in a limited durability of the adsorbent material not to allow repeated use.
Another proposal is made in Japanese Patent Kokai 8-71415 for the preparation of an ion exchange resin-based adsorbent material in which zirconium ions are supported on a cation exchange resin by using an aqueous solution of a zirconium compound. This method is also defective because, since the zirconium ions are supported on the cation exchange resin by bringing the ion exchange resin into contact with an aqueous solution of a zirconium compound to effect an ion exchange reaction, the amount of zirconium ions supported on the ion exchange resin is inevitably limited and, as a consequence of the low temperature at the thermal treatment which is 100.degree. C. or lower, the hydrous zirconium oxide is in an amorphous form or has a low degree of crystallinity so as to be readily eluted out of the supporting ion exchange resin.